Electric discharge apparatus



Oct. 14, 1941. R. c. KELTING 2,259,069

ELECTRIC DISCHARGE APPARATUS Filed Nov. 20. 1940 Figl.

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Inventor:

Richard C. Kelting,

Patented Oct. 14, 1941 I ELECTRIC DISCHARGE APPARATUS Richard C. Kelting, Orange, N. 3., assignor to General Electric- Company, a corporation of New York Application November 20, 1940, Serial No. 366,421

2 Claims. (Cl. 176-124) My invention relates to electric discharg devices such as discharge lamps'and apparatus associated therewith for starting and operating the same.

With lamps of this type as with lamps in general it is common to employ reflectors for directing the light thereof in a direction in which it is most needed. In the case of a discharge lamp and control apparatus therefor such as that disclosed in the Foulke Patent 2,177,883, it has been found that when the lamp is provided with a metal reflector attached to the frame or housing supporting the control apparatus a premature starting of the lamp sometimes occurs, that is, the discharge in the lamp may be started before the cathode has reached an electron emitting temperature. Such premature starting of the lamp is due principally to the electrostatic effect of the reflector near the lamp in that when a sufficient voltage exists between the reflector and the electrodes of the lamp, particularly the anode connected directly with the operating circuit, anode 3, rather than the other anode which connects through the starting delay mechanism, the gas in the lamp becomes ionized enough to permit it to break down and allow an arc to strike between the direct connected anode 3 and the cathode before the delay mechanism functions. It is the object of my invention to provide improved control apparatus having means for preventing such premature starting of the lamp.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a side view illustrating one embodiment of my invention and Fig. 2 is a circuit diagram thereof. In the drawing, I is an electric discharge lamp having at one end the thermionic filamentary cathode 2 and at the other'end the anodes 3 andt separated by the baflie 51 Arranged adjacent the lamp is the reflector 6 which is shown having those portions cut away which hide the lamp electrodes. The reflector is mechanically and electrically connected with the frame or casing I which supports and encloses the auxiliary apparatus for starting and controlling the operation of the lamp. This starting and controlling apparatus is represented diagrammatically below the lamp in Fig. 2 where the frame or casing is indicated by the dotted rectangle 1'. The starting and controlling apparatus which I employ is the same in construction and operation with that shown and described in the above-mentioned Foulke Patent 2,177,883.

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It comprises the unitary structure 8 which includes a combined high reactance transformer The core of the structure is made up of the two E-shaped members 9 and I0 reversel-y arranged with respect to each other and with corresponding legs spaced from each other to form magnetic gaps. Between the legs of the member ID are the magnetic shunts I I to increase the flux leakage thereby to provide higher leakage reactance.

On each of the outer legs of the core structure is a primary winding consisting of the coil I2, a main secondary winding consisting of the coil I3 plus th coil I2 thereby constituting an auto-transformer and a secondary auxiliary winding comprising the coils Id. The ends of the primary thus composed of the two coils I2 are connected by the leads I5 and switch I6 with the opposite sides of a source of current supply. The opposite ends of the main secondary composed of the two coils I2 and the two coils I3 connect with the two anodes 3 and l, one directly and the other through a switch which will be described hereinafter, and the mid-point thereof connects with the cathode 2. The latter connection includes the conductor I1 and the auxiliary secondary made up of the two coils It, the purpose of which is to supply heating current to the lamp cathode.

As shown by the drawing, the magnetic shunts II are arranged adjacent the upper ends of the primary coils and extend between the outer legs of the core structure and the middle leg I8 thereof, said shunts being spaced from those legs by magnetic gaps which preferably comprise suitable non-magnetic material. The purpose and function of thismagnetic structure is the same as described for the corresponding parts in the above-mentioned Foulke patent. As in that patent also, the capacitor 2 3 which is used to improve the power factor of the unit and assist in starting the lamp is connected across the secondary of the transformer in series with a suitable reactance. The reactor or choke coil 25 which has the intermediate tap 26 dividing it into the two parts 21 and 28, functions as an autotransformer in the manner fully described in the aforementioned Foulke patent. As in that patent the reactor 25 preferably comprises the E-shaped member 29 which is separated from .the transformer core by the magnetic gaps 30.

For controlling the starting and running of the lamp I there is provided the electromagnetic switch 32 having th armature 36 arranged adjacent the gap '31 and operating between the v contacts 33 and 34, the switch being held in a retracted position by means of the spring 35. As in the aforementioned Foulke patent the switch 32 is moved from the starting position illustrated tothe operating position by the flux through the air gap 31 after the lamp is started. For providing the desired time delay to enable the cathode 2 to become heated to an electron emitting'temperatur before the starting voltage is applied to the lamp, I have shown the time delay mechanism comprising the, three bimetallic blades 38, 39 and 40, the blade having thereon the high'resistance heating coil 4| and the blade' 40 having thereon the low resistance heating coil 42. This time delay mechanism, it will be understood, operates in exactly the same manner as in the aforesaid Foulke patent.

Inasmuch as apparatus of this character ordinarily is connected to be supplied through a distribution transformer, I have represented such a transformer at 44, the secondary 45 of which is shown connected with the leads l5. As is well known to those skilled in the art, it is usual to ground one end or the other or the mid-point of the secondary of the distribution transformer. I have found that when the end marked A of the distribution transformer secondary is grounded no trouble is experienced with pre-starting of the lamp since in that case the voltage appearing between the reflector and the direct connected anode 3 of the lamp is only that which appears across one secondary coil l3. However, when the mid-point B of the secondary is grounded an appreciable percentage, of pre-starts under certain conditions have occurred and when the end marked C'ofthe secondary is grounded a. higher percentage of pre-starts under such conditions have occurred. In the last mentioned case it will be noted that the voltage between the reflector and the anode 3 is that appearing across the entire primary plus the one secondary I; which connects with that anode.

To prevent any prestarting of the lamp when either the mid-point B or the end C of the distribution transformer secondary is grounded, I provide the small capmitor 46 whose capacitance for example may be from .03 to .05 mid. and connect this capacitor by the lead 41 between the reflector 6 and the point t8, the junction between the primary coil i2 and the secondary coil i 3 connecting with the anode '3, it being remembered that the frame 1 and the reflector 6 are electrically connected with each other. As a result of this capacitive connection the voltage appearing between the reflector and the anode 3 is never greater than that across the secondary coil i3 regardless of what point on the distribution transformer secondaryis grounded,which voltage is insuflicient' to cause a prestarting of the lamp.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric discharge lamp comprising an enclosing envelope having a cathode and a plurality of anodes therein, a stepup auto-transformer having the ends of its secondary arranged to be connected each with one of said anodes and its mid-point with said cathode, means for preheating said cathode, time delay means for applying a starting voltage between one of said anodes and said cathode, a reflector supported adjacent to said lamp and subject to cause premature starting thereof by capacitive action therewith and means for pre-- venting said premature starting of said lamp comprising a capacitor operatively connected between said reflector and that end of the primary of said transformer whose voltage is nearer to that of the other of said anodes.

2. In combination, asupporting frame, an electric discharge lamp thereon comprising an enclosing envelope having a cathode and a plurality of anodes therein, a step-up auto-transformer on said frame having means for applying a preheating current to said cathode,means connected between one end of the secondary of said transformer and one of said anodes for applying a starting voltage to said lamp after a predetermined time delay, a connection between the other end of said secondary and the other of said anodes, a reflector supported by and electrically connected with said frame and arranged at that side of said lampadj acent to said other anode and means for preventing the starting of said lamp because ofthe presence of said reflector prior to the application of said starting voltage comprising a capacitor connected between said frame and that end of the primary of said transformer whose voltage is nearer to that of said other anode.

RICHARD C. KELTING. 

